High velocity dryer tube



May 26, 1964 A. G. RUSSELL HIGH VELOCITY DRYER TUBE 5 Sheets-Sheet l Filed March 27. 1961 1NVENToR LFEED G. PUSSELL,

BY 47 IQTTOQMEY May 26, 1964 A. G. RUSSELL HIGH VELOCITY DRYER TUBE 5 Sheets-Sheet 2 Filed March 27, 1961 INVENToR.

HL FRED f RUSSELL BY i M ATTORNEY May 26, 1964A A. G. RUSSELL 3,134,654

HIGH VELOCITY DRYER TUBE Filed March 27. 1961 5 Sheets-Sheet 3 INVENTOR. LFPEDQPUSSELL,

BY M

H TTOQA/E Y May 26, 1964 A. G. RUSSELL HIGH VELOCITY DRYER TUBE Filed March 27, 1961 5 Sheets-Sheet 4 IN VEN TOR. HLFRED 6?. PUSSELL BY M I y J ATTORNEY A. G. RUSSELL HIGH VELOCITY DRYER TUBE 5 Sheets-Sheet 5 @TTG/2HE Y May 26, 1964 Filed March 27, 1961 United States Patent O 3,134,654 Hill-H VELGCHY DRYER TUBE Alfred G. Russell, Martinsville, NJ., assigner to Frank W. Egan t Company, Somerville, NJ., a corporation oi New .lersey Filed Mar. 27, 196i, Ser. No. 98,387 Claims. (Cl. 34--160) This invention relates in general to apparatus for treating strip or web material such `as fabrics, papers, pulp and `other liquid containing or coated materials, by means of a iuid such .as steam, air, or other gases, and more particularly the invention is directed to `apparatus such as high velocity dryers Ithat include -large conduits or headers for supplying the treating fluid such as air, and elongated fluid-distributing tubes, each having at least one inlet end connected to and communicating with at least one of the headers or conduits and also having restricted outlet openings spaced apart longitudinally ofthe tube or Ian elongated outlet slot extending longitudinally of the tube for `directing the treating fluid at high velocity onto the web, sheet, or strip to be dried or otherwise treated. The invention especially contemplates an improvement in duid-distributing tubes ifor apparatus of the type described in my co-pending application Serial No. 968, now `Patent No. 3,036,385, tiled January 7, 1960, wherein there .are a plurality of elongated air-distributing tubes in a housing that are rectangular in crosssection and are closely spaced from each other, each with an inlet at one end connected to and communicating with a duid supply header and having a plurality of outlet slots in one wall thereof aligned longitudinally of the tube so that liu-id is conducted :from the supply header to the material being treated and ilows after contact with the treated material between the .tubes land thence into the atmosphere, lfor example, through exhaust ducts or plenums.

it has been noticed in the use of the tube type high lvelocity drying system that there is a temperature inequality of the supply air due to the very large heat transfer rates possible with this type drying system. There `are two important temperature difference with which the present invention is concerned, one difference being between the air inside the distributing tube and the spent air outside the tube lafter the air has contacted the web; and the Iother temperature difference occurs in the supply `air .inside the distributing tube between the feed or inlet and the portion of the outlet farthest `trom the inlet. With end fed tube type drying systems, the supply air impinges on the web, then passes between successive tubes back to the exhaust and recirculation plenums. Prior experience has not brought this inequality to light in-asmuch as the drying eiliciency of earlier systems did not approach that of the presently known systems, in operation of which with high drying loads, the temperature of iiuid issuing from the outlet `slots at the header end of the tube may be as much `as 30 to 40 F. higher than that issuing -fr-omthe closed end, When highly efficient drying means possible wit-h known high velocity tube type drying systems are subjected to heavy drying loads, ie., are used to evaporate large quantities of water from a web, there is a signiiicant heat transfer between the supply air and the web. 'Ihis causes a drop in the temperature of the supply air relative to the temperature ofthe exhaust air that can be as high at 100 to 200 F., idepending upon the initial temperature. This is one temperature diierence between the air inside and the spent air outside the tube causes a heat transfer :between the tube walls which results in loss in temperature of the supply air. Another temperature diilerence which may be of the order of about 70 degrees occurs in the sup- 3,134,654 Patented May 26, 1964 ply air in the distributing tube between the feed or inlet and `the portion of the outlet farthest from the inlet; in other words, the air which issues from the outlet slot, the farthest from the inlet end has to pass a lgreater distance along the relatively cool outer walls, and therefore gives up more heat, resulting in lowering of its temperature relative to the supply air which issues from the slot nearest the `feed end. The use of end fed tubes lwherein the spent air passes from the web between successive tubes improves the air ow characteristics in the drying of continuous Webs, and the present .invention permits the use of this efficient .tube ted drying means in applications where high drying rates are experienced. The present infvention includes alternate methods of correcting this inequality, based on the anticipated heat transfer and resultant temperature difference between the supply and exhaust air, to insure essentially equal supply lair temperatures across the width of the slot irrespective of the difference in supply and exhaust air temperature.

lt will a'lso be understood yby those skilled in the art that it is desirable that the velocity of the fluid be substantially luniform at the outlets so that the portions of the material being treated that -lie `farthest yfrom the inlet of the tube will be subjected to essentially the same temperature and velocity of air as the other por-tions of material nearer the inlet.

Therefore, primary objects of the present invention are to provide apparatus of the character described including a Huid-distributing tube constructed in a novel and improved manner providing ifor substantially equal or uniform -iiuid temperature at all `of the discharge openings throughout the length of the tube; and to provide such a tube, the consuuct-ion of which shall be such that the equality or uniformity of the Huid temperature shall be obtained without material effect upon the velocity of ilow of the iluid from the outlets.

IFurther objects `are to provide an air-distributing tube of the character described which `shall have therein a novel and improved bafe disposed between the inlet and the outlet of the tube such that the length of the path of travel of the fluid from the inlet to the outlet shall be different at different zones in the length of the tube, and thus to provide in the tube a baille which shall cause the iluid emerging from the outlets nearer the inlet to travel yfrom the inlet to the outlet a greater :distance along the relatively cool outer wall of the tube than does the iluid emerging from the zone of the outlet farthest from the inlet and thereby equalize the cooling effect on the air issuing `from the tube at all points along the length of the tube.

Still another object is to provide such a tube wherein the baille is so constructed and arranged as to insulate the warm iluid within the tube against the cooling effects of the uid that Hows outside and between the tubes from contact with the material being treated to the eX- haust ducts, particularly where the temperature difference between the supply air and the outside air is relatively small.

Other objects, advantages and results of the invention will be brought out by the following description in conjunction with the accompanying drawings in which:

FIGURE l is a schematic transverse Vertical sectional View through a high velocity tube-type dryer including a housing in which are a plurality of huid-distributing tubes embodying the invention, said ligure being similar to FIGURE l of my above-mentioned co-pending application, Serial No. 968;

FIGURE 1A is a schematic sectional view approximately on the plane of the line 1a of FIGURE l;

FIGURE 2 is an enlarged perspective view of a fluiddistributing tube removed frorn the housing shown in FIGURE l and with portions broken away and other portions shown in section for clearness in illustration;

FIGURE 3 is a further enlarged transverse vertical sectional view approximately on the plane of the line 3--3 of FIGURE 2;

FIGURE 4 is a similar view on the plane of the line 4-4 ot FIGURE 2;

FIGURE 5 is a view similar to FIGURE 4 on the plane of the line 5-5 of FIGURE 2;

FIGURE 6 is a central longitudinal vertical sectional view through a huid-distributing tube embodying a modilied form of the invention, the baille being shown in side elevation with portions broken away;

FIGURE 7 is an enlarged transverse vertical sectional view on the plane of the line 7-7 of FIGURE 6;

FIGURE 8 is a view similar to FIGURE 6 showing another modilication of the invention;

FIGURE 9 is an enlarged transverse vertical sectional view of the whole tube on the plane of the line 99 of FIGURE 8;

FIGURE l0 is a similar view on the plane of the line 13-16 of FIGURE 8;

FIGURE ll is a View similar to FIGURE 8 showing another form of the invention;

FIGURE 12 is an enlarged transverse vertical sectional view through the whole tube approximately on the plane of the line i2 i2 of FIGURE 1l;

FIGURE 13 is a view similar to FIGURE 11 showing another modification of the invention; and

FIGURE 14 is a view simiiar to FIGURE 2 on the plane of the line ltd-14 of FIGURE 13.

While the invention has been illustrated in connection with the generally known type of apparatus for drying or otherwise treating strip materials or webs, it should be understood that the invention may be embodied in other types of Huid-distributing tubes for other material treating apparatus, and while the huid-distributing tube embodying the present invention has been shown in conjunction with apparatus like that shown in my co-pend ing application wherein the material to be treated is in the form of an elongated web moved by an endless conveyor through the housing between two banks of distributing tubes, the invention resides in the construction of a single tube which may be used alone or in conjunction with other tubes for drying, for example, webs or strips moved on conveyors or separate pieces placed in and removed from the dryer housing manually or in some other way.

Specically describing the embodiment of the invention illustrated in FIGURES l through 6, the reference character A generally designates a housing or casing providing therein a treatment chamber through which a strip or web of material B is conveyed in horizontal position by a suitable conveyor which in the present instance is shown as including two horizontally spaced chains C slidably mounted on tracks D within the housing and driven by suitable means such as sprockets G and power operated drive means such as a motor (not shown), the chains supporting cross bars E that are spaced apart longitudinally of the chains and may have connected thereto helical springs F or the like on which the web B is laid so that there is a minimum of area of contact between the web and the conveyor. One track D is shown as mounted on a vertical frame piece 1 in the housing while the other track D is shown as mounted on the inner side of one of two supply conduits or headers H for the treating iluid such as steam or air.

While in many cases only one bank of Huid-distributing tubes is required, in the present instance, two horizontal banks of tubes I and I have been shown, one bank above and one bank below the web B, and each of the tubes of one bank has one end connected to one of the headers H while each tube or the other bank has one end connected to the other header H'; and the treating fluid is conducted from the headers through the respective tubes I and I' and their outlets J into contact with the corresponding sides of the web B, whereupon the treating iluid passes into outlet or exhaust ducts K and K' through slots K.

While the tubes may be mounted in any suitable manner in the housing and connected to thc supply pipe or header in different ways, for the purpose of illustration here, each tube is removably mounted in the apparatus and has one end held in separably connected relation to the corresponding header under yielding or spring pressure.

As shown in my co-pending application, one vertical wall 2 of each header has an opening 3 therein to receive each tube, and each tube has a stop member or flange 4 in spaced relation to the end of the tube to abut the side wall of the header and limit insertion of the inlet end of the tube into the opening 3 as best shown in FIGURES 1 and 6.

The other end of each tube is separably connected to the support frame by a connector device L.

As will be readily understood by these skilled in the art, access to the tubes for insertion and removal thereofv may be had through a suitable access opening A that is normally closed by a door A.

The construction of the fluid-distributing tube I may be varied, but as shown, the tube is rectangular in cross-section and has an end wall 6 opposite the inlet end, side walls il, a top wail l2, and a bottom wall i3 intermediate the width of which is a discharge opening or outlet which is formed by integral parallel lips 14 projecting from the bottom wall and rigidly held in pre-determined spaced apart relation by spacer blocks 15 that are disposed in spaced relation to cach other longitudinally of the lips. With this construction, a portion or the outlet of cach tube comprises an outlet or discharge opening etween each two adjacent spacer blocks but the opcnings are closely spaced and staggered in successive tubes so that, in effect, there will be a substantially continuous sheet of warm fluid discharged from each tube into contact with the sheet or web of material B being treated.

Obviously, the dimensions of the tubes will vary according to the conditions of intended use, as will also the lips 14 and the spacing of the blocks l5. The ratio of cross-sectional area of the tube to the arca of the discharge openings may be varied but preferably is such as to obtain substantially equal or uniform uid distribution through the discharge openings along the length of the tube. Experience shows that desirable ratios are of 2.5/1 upward to lO/l, the most desirable ratio being between 5/1 and 8/1.

It will be noted that the plurality of tubes I in a bank are closely spaced apart and that the uid discharged from the discharge opening J contacts with the material being treated and gives up heat which reduces its temperature whereupon it tlows between the tubes to the exhaust ducts as shown schematically in FIGURE la and thus produces a cooling eilect on the iiuid in the tubes; and it will also be observed that unless some means is provided to prevent it, the temperature of the iiuid in the tube will gradually decrease during the ow of the i'luid from the inlet end of the tube to the opposite end thereof. It should be understood that the cooling eiiect is a relative matter and there will be heat transfer and temperature inequality, for example, with a supply air temperature of 700 F. which cools to 600 F., and there will also be heat transfer and temperature inequality where the supply air has a temperature of F. and is cooled to 70 F. The differences in temperature between the supply air and the exhaust air with known constructions is most likely to occur where a heavy drying load is impressed upon the drying apparatus.

As hereinbefore indicated, the invention provides a Huid-distributing tube embodying a novel and improved construction which will ensure substantial equal or uniform temperature of the iluid owing from the discharge ena/geen D openings of the tube throughout the length of the tube, and more particularly, the invention contemplates a baffle that is inserted into the tube. One form of the invention is shown in FIGURES 1 through 5 inclusive .where the baille comprises a rectangular tube M open at one end and having a wall M at its other end, side walls 16 and 17, a top wall 13, and a bottom wall 19, all preferably in equidistantly `spaced relation to the corresponding walls of the tube I. The inlet end of the baille tube has an exterior perimetral flange 20 snugly tted within the tube I so as to close the space between the walls of the two tubes and ensure that iluid shall ilow from the supply header only into the baille tube. The baille tube has outlet apertures 21 arranged in its walls so that the iluid from inside the baille tube will ilow through said apertures into the spaces between the baille tube and the distributing tube and the length of the path of flow of the iluid from the outlet apertures 21 to the discharge openings J will vary between the inlet of the distributing tube and the other end thereof. Thus, a series of outlet apertures 21a is provided in the top wall 1S of the baille tube adjacent the inlet of the distributing tube, another series 21h of outlet apertures are formed in the side walls 16 and 17 of the baille tube and extend in an approximately straight line from the top wall to the bottom wall as best shown in FIGURE 2, t a point in spaced relation to the closed end `of the distributing tube; and a third series 21C of outlet apertures is provided in the bottom wall 19 of the baille tube between the apertures 2lb and the end of the tube. The rows of apertures 21a and 21C also preferably extend diagonally from the side walls to the centers of the top and bottom walls, respectively. With this construction, it will be observed that the path of ilow of iluid along the relatively cool outer walls 11, 12 and 13 4from the apertures 21a to the discharge openings I will be substantially greater than the distance of travel of the iluid along said cool outer walls from the outlet apertures 21C to the discharge openings I, and the distances of travel along said cool outer walls from the apertures 2lb to the discharge openings J will gradually decrease from the apertures 21a to the apertures 21o. These paths of ilow are indicated by the arrows in FIGURES 3, 4 and 5 of the drawings.

A modified form of the invention is shown in FIG- URES 6 and 7 wherein the baille insert N is in the form of a channel having a continuous ilange 22 at one end corresponding to the ilange and having its bottom wall 23 parallel and in spaced relation to the bottom wall 13 of the distributing tube I with its side walls 24 disposed in spaced and parallel relation to the corresponding side walls of the distributing tube I and gradually decreasing in height or width from the inlet end of the distributing tube to the opposite or closed end 6 thereof. Desirably, the end of the bottom wall 23 of the baille insert may have an extension tongue 25 secured to the end wall 6 for supporting that end of the baille.

With this construction, it will be observed that the iluid will ilow from the header into the baille N and upwardly over the edges of the side walls 24 of the baille and thence downwardly to the discharge openings J of the distributing tube as schematically illustrated by the arrows in FIGURE 7; and due to the decreasing height of the side walls 24, the lengths of the paths of ilow of the lluid from the inlet end of the distributing tube to the discharge openings J adjacent said inlet end will be substantially greater along relatively cool surfaces 11 than the lengths of the paths of ilow of the iluid from the channel of the baille over the edges of the side walls thereof tothe discharge openings at the other end of the distributing tube.

FIGURES 8, 9 and l0 show another form of the invention where one of the distributing tubes I is illustrated with its discharge openings I facing upwardly instead of downwardly as in tubes I lin FIGURES 1 through 7 inclusive. In this form of the invention, the baille O is shown as comprising two side walls 27 extending through- CSX out the length of the tube having ilanges 2S at their longitudinal edges to space the side walls 27 from the corresponding walls of the distributing tubes I'.

There is a partition 29 connecting and between the side walls throughout about half the length and about centrally of the height thereof. A vertical partition 30 extends bet-Ween the inlet end of the baille, the side walls 27, and the bottom wall of the distributing tube. With this construction, the iluid from the header ilows through the inlet of the distributing tube between the partition 29 and the wall of the distributing tube opposite the discharge openings as indicated by the arrows in FIGURE 8. Some of the iluid continues -to ilow toward the closed end of the distributing tube while the direction of flow of the other portions of the iluid is reversed so that said portions ilow backwardly along the partition 29 and outwardly through the discharge openings I, all as indicated by the arrows in FIGURE 8. Thus, the difference in distance and direction of ilow of the fluid at different points in the length of the tube and the insulating spaces between the tube walls 11 and baille walls 2'7 ensure that the temperature of the iluid throughout the discharge openings I shall be substantially uniform.

As above stated, the spaces between the side walls 27 of the baille O and the corresponding side 'walls of the distributing tube serve as insulating spaces, and it will be observed that in addition to the variations in the length and direction of the paths of ilow of the iluid for providing essentially uniform temperature of the iluid in all of the discharge openings, other forms of the invention also utilize the insulating property of some of the spaces between the walls of the baffle and the walls of the distributing tube to reduce the cooling effect on the iluid in the tubes of the iluid ilowing along the outer sides of the walls of the tubes. For example, in the form of the invention shown in FIGURES 1 to 5 inclusive, the space between the side walls 16 of the baille tube and the side walls 11 of the distributing tube, as well as the spaces between the side walls 18 and the top wall 12 of the distributing tube between the outlet apertures 21a and the closed end of the distributing tube, insulate the walls 16 and 18 of the baille tube against the relatively cool air in Contact with the outer surface of the side walls 11 and top wall 12 of the distributing tube.

FIGURES 11 and 12 show another form of the invention somewhat similar to the form shown in FIGURES 8 to 10 inclusive except that the side walls 32 of the baille P extend the full length of the distributing tube and the partition 33 extends throughout the length of the distributing tube and is inclined from the inlet end of the tube toward the opposite end thereof in such a way that the volume of Athe space for ilow of iluid from the inlet through the discharge openings decreases gradually from the inlet end of the tube to the opposite end thereof. The spaces between the side walls 32 of lthe baille and the corresponding side walls of the distributing tube serve as insulating spaces.

FIGURES 13 and 14 show still another form of the invention wherein the baille Q comprises two side walls 34 similar to the side walls 32 that are spaced from the corresponding side walls of the distributing tube and are connected adjacent their upper ends by a partition 35 that extends from the inlet end of the baille to a point spaced from the opposite end thereof at which there is another partition 36 in spaced relation to the end wall 6 of the distributing tube. At the inlet end of the baille is a ilange 37 that closes the space between the side walls of. the distributing tube and the baille and between the top wall of the distributing tube of the partition 35 of the baille. With this construction, there are insulating spaces between the top wall of the distributing tube and the partition 35 of the baille, also between the side walls of the baille and the side walls of the distributing tube and between the end wall of the distributing tube and the partition 36.

3,13 ses While the fluid-distributing tubes embodying the invention may be satisfactorily used under diiierent conditions, it can be said that the inveniton has been found especially satisfactory in tubes having a discharge slot or opening about ninety inches in length and' operating with an air temperature diiierenee up to 220o F. between the air supply at the inlet `and the ambient air outside the tubes, giving less than a F. temperature difference between the end of the discharge opening nearest the tube inlet and the opposite end of the tube. Without the baffles, the temperature difference may be as great as 50 F. Furthermore, from experience with the form of the invention shown in FIGURES 6 and 7, it has been found that the air velocity proiile gives a variation of less than two percent if the area ratios of inlet to discharge is greater than five or six to one.

it has also been found that the tubes like those shown in FIGURES 11 to 14 inclusive utilizing the double wall insulating characteristics, ensure only a slight decrease in the temperature of the fluid from the inlet end to the closed end of the tube, which varies with the inside and outside temperature and the quantity of air flowing through the tube.

lt will be understood that the bailiing means embodying the invention can be used in extremely wide tubes fed with heated supply air from both ends, which would have the same relative effect as a tube of half the length which was fed from one end. Also, with a tube fed from both ends, as shown, for example, in FIGURE of my co-pending application Serial No. 968, now Patent No. 3,036,385, there could be two identical baille units, for example, like the one shown in FGURES 2 and 6 of the present application, one at each end of the distributing tube with its inlet end communicating with the inlet end of the tube.

While several structural embodiments of the invention :u e been illustrated and described, it should be understood by those skilled in the art that the details of construction of the distributing tubes may be widely modified and changed and that the invention may be embodied in other types of huid-distributing tubes as well as in iluiddistributing tubes for other purposes, within the spirit and scope of the invention.

I claim:

1. A fluid distributing tube for use in apparatus for treating material with a heated gaseous uid, said tube having at least one inlet at an end thereof for connection to a supply of heated iluid under pressure and also having an outlet extending longitudinally of the tube between said inlet and the other end of the tube, and means comprising a baille inside said tube having walls spaced from the side walls of the tube substantially throughout the length of the outlet forming iluid spaces between the baille walls and the walls of said tube and also forming an inlet passage for fluid from said inlet to said outlet, said bame walls providing between them and the relatively cool outer walls of said tube paths along the length of said baffle Walls each directly from said inlet passage to said outlet, the lengths of which paths along said outer walls from said inlet passage to said outlet gradually decrease from said inlet to the point in said outlet farthest from said inlet, providing for maintenance of the temperature of the fluid from said inlet substantially uniform from said inlet to the point in the outlet farthest from the inlet throughout a wide range of temperature differences between the temperature of the fluid supply at the inlet and the temperature of the fluid outside the tube.

2. A fluid distributing tube as set forth in claim 1 having top, bottom and side walls and said outlet in the bottom wall, and wherein said baille is channel shaped and has its bottom wall in spaced and parallel relation to the bottom wall of the tube in juxtaposition to said outlet, and the side walls of the channel are disposed in spaced and parallel relation to the corresponding side walls of the tube and decrease in height from the inlet end of the tube toward the other end thereof, and said baille has a flange at its larger end coacting with the Walls of the inlet end of the tube to cause the lluid to flow into the tube only through the baille.

3. A fluid distributing tube as defined in claim 1 wherein said baille is tubular and has one open end coincident with the inlet of the distributing tube and its other end closed, the side walls of the tubular baffle having outlet apertures the distances between which and the outlet gradually decrease from the inlet of the tube toward the point in the outlet farthest from the inlet.

4. A fluid distributing tube as defined in claim 3 wherein both the distributing tube and the tubular baille are rectangular in cross-section, the outlet of the tube is in the bottom wall of the tube the outlet apertures nearer the inlet end of the tuoular baille are in a top wall of the baille farthest from the discharge openings, other outlet apertures are disposed in the side walls of the tubular baille and at distances 'from the outlet that decrease from the first-mentioned apertures toward the other end of the tube.

5. A fluid distributing tube as defined in claim 3 wherein both the distributing tube and the tubular baille are rectangular in cross-section with top, bottom and side walls and said outlet of the tube is in the bottom wall of the tube, the outlet apertures of the baille nearer the inlet end of the tube are in the top wall of the baille farthest from the outlet, other outlet apertures are disposed in the side walls of the baille and at distances from the outlet openings that decrease from the first-mentioned apertures toward the other end of the tube, and the bottom Wall of the baille has outlet apertures adjacent the second-mentioned end of the tube and extending diagonally thereof from said side wall of the baille toward the other side.

Cohn et al. July 8, 1952 Meltzer et al Nov. 10, 1953 

1. A FLUID DISTRIBUTING TUBE FOR USE IN APPARATUS FOR TREATING MATERIAL WITH A HEATED GASEOUS FLUID, SAID TUBE HAVING AT LEAST ONE INLET AT AN END THEEREOF FOR CONNECTION TO A SUPPLY OF HEATED FLUID UNDER PRESSURE AND ALSO HAVING AN OUTLET EXTENDING LONGITUDINALLY OF THE TUBE BETWEEN SAID INLET AND THE OTHER END OF THE TUBE, AND MEANS COMPRISING A BAFFLE INSIDE SAID TUBE HAVING WALLS SPACED FROM THE SIDE WALLS OF THE TUBES SUBSTANTIALLY THROUGHOUT THE LENGTH OF THE OUTLET FORMING FLUID SPACES BETWEEN THE BAFFLE WALLS AND THE WALLS OF SAID TUBE AND ALSO FORMING AN INLET PASSAGE FOR FLUID FROM SAID INLET TO SAID OUTLET, SAID BAFFLE WALLS PROVIDING BETWEEN THEM AND THE RELATIVELY COOL OUTER WALLS OF SAID TUBE PATHS ALONG THE LENGTH OF SAID BAFFLE WALLS EACH DIRECTLY FROM SAID INLET PASSAGE TO SAID OUTLET, THE LENGTHS OF WHICH PATHS ALONG SAID OUTER WALLS FROM SAID INLET PASSAGE TO SAID OUTLET GRADUALLY DECREASE FROM SAID INLET TO THE POINT IN SAID OUTLET FARTHEST FROM SAID INLET, PROVIDING FOR MAINTENANCE OF THE TEMPERATURE OF THE FLUID FROM SAID INLET SUBSTANTIALLY UNIFORM FROM SAID INLET TO THE POINT IN THE OUTLET FARTHEST FROM THE INLET THROUGHOUT A WIDE RANGE OF TEMPERATURE DIFFERENCES BETWEEN THE TEMPERATURE OF THE FLUID SUPPLY AT THE INLET AND THE TEMPERATURE OF THE FLUID OUTSIDE THE TUBE. 